Centrifugal switch



Sept 8, 1970 P. P. scHwAB 3,527,906

. CENTRIFUGAL sw'ITcH Filed June'; 1969 FIG. l FIG. 2`

1 f 20 il@ f 5-2/ 1 l l l 0 Hal' al-- g f f26 23i/4- 1', 5 if?? 5 ,12j NW9 /2 f I2 /fff y/,l ff//f 9,23 lla 257 (I7 l /3 v l! l i H /fr /6 l ll: l Il! l( Q 'i L. b \l t t5 Q D I l I Gs cEA/rR/FUGAL FORCE mvsNToR PIERRE P. SCHWAB AGENT United States Patent O 3,527,906 CENTRIFUGAL SWITCH Pierre P. Schwab, River Edge, NJ., assignor to McGraw- Edison Company, Elgin, lll., a corporation of Dela- Ware Filed .lune 6, 1969, Ser. No. 831,144 Int. Cl. H0111 35/10 ABSTRACT F THE DISCLOSURE A miniature centrifugal switch of a rugged shockproof construction is provided for triggering ballistic fuses of projectiles. The switch comprises a metal cylindrical case mounted for revolving movement about an axis parallel to its longitudinal axis. A movable conductive mass serving also as a switch contact is mounted on an end wall of the case through a helical spring to permit the mass to be deflected sidewise by centrifugal force. However, the spring is pretensioned-i.e., wound tightly on itselfso that the mass is not deflected by increasing centrifugal force until a predetermined rotational speed is reached about an axis parallel with the central longitudinal axis through the helical spring and mass.

The design requirements for ballistic switches are extremely rigid in that the switches must be of miniature size, must meet rigid shockproof and vibration proof requirements, must experience no physical change after years of storage under wide temperature and humidity conditions, and must operate dependably within close limits of a specified rotational speed.

An object of the present invention is to provide a novel and economical design of a centrifugal switch which meets these rigid requirements.

Other objects and features of the invention will be apparent from the following description and the appended claims.

In the description of my invention reference is had to the accompanying drawings, of which:

FIG. l is a view showing the mounting of the present centrifugal switch device relative to its rotational axis;

FIG. 2 is a diametrical sectional view of the switch device taken along its longitudinal axis;

FIG. 3 is a cross sectional view taken on the line '3 3 of FIG. 2; and

FIG. 4 is a plot of contact-mass deflection versus centrifugal force during the revolving of the switch.

The present centrifugal switch device has a cylindrical case comprising a cylindrical cup 11 formed by deep drawing as of nickel-plated copper. The cup is formed during the drawing Operation with flanged edge 11a at its open end. Typically, the size of the case is approximately .2" long and .21" in diameter. The case has a shallow cup-shaped header 12 of Kovar metal (nickeliron alloy) fitted into the open end of the cup 11. The header has a peripheral radially extending rim 13 which is seated against the rim 11a of the cup 11 and is welded or braised thereto. The central portion of the header is formed with an annular inwardly extending flange 14 forming a central cylindrical opening 15. A rst terminal pin 16 extends centrally through the opening 15 and is sealed to the header by a glass medium 17. A second terminal pin 18 is braised at 19 to the header 12 and encased at its tip also by the glass medium 17 The header 12 constitutes a supporting base for the internal parts of the switch, permitting the switch therefore to be fully assembled on the header before the latter is mounted on and braised to the cup 11. The switch com- 3,527,906 Patented Sept. 8, 1970 ice prises a cylindrical mass 20 having an axial opening 21 extending therethrough and having a cylindrical extension 22 at its outer end, which is of reduced diameter equal to that of the flange 14 on the header. The mass 20 has a clearance spacing on all sides from the case 10 and occupies about 50% of the internal space in the case. The mass is made of any suitable material having the desired specific gravity, and is nickel and gold plated to provide it with good surface conductivity, since it serves also as a contact of the switch, as will appear.

A helical spring 23 is pressed at one end onto the flange 14 and at the other end onto the extension 22 of the mass 20, and may be braised at both ends to these parts. This spring provides a yieldable support on the case for the contact mass 20. The spring convolutions are wound tightly onto each other to pretension the spring so that it tends to hold the mass rigidly in centered relation to the case. However, as will appear, a sidewise force on the mass lateral of the case may bend the spring sidewise allowing a sidewise deflection of the mass when the force exceeds a critical value.

The central pin 16 extends longitudinally through the mass 20 with a clearance spacing from the wall of the axial opening 21. This pin has a frustoconical tip 24 at its end which is at a uniform spacing from the surrounding wall 25 of the opening 21. The terminal pin 16 is preferably made of Kovar and the tip 24 thereof is nickel and gold plated since it serves as a contact of the switch. When the switch is closed electrical connection is made between the terminal pins 16 and 18` via the header 12, spring 23 and contact mass 20. The use of nickel and gold plating of the portions forming the switch contacts assures very low resistance between the contacts under light pressure and protects the contact areas from film formations which would increase 'the contact resistance. Further, to this same end, the case 10 is evacuated of air and is then filled with inert nitrogen preferably also with some helium for leak detection purposes. Low electrical resistance from the contact mass 20 to the terminal pin 18 is achieved by using a stainless steel spring 23 which is copper flashed and also nickel and gold plated and by both nickel and gold plating the flange 14 on the header 12.

As is shown diagrammatically in FIG. l, the present switch device is mounted with its base end flat against a support 26. The terminal pins 16 and 18 extend through the support-which may be a printed circuit board--and are secured thereto as by soldering. Additionally, the case may be secured to the board as by an epoxy resin 27. The support 26 is considered as having a rotational freedom of movement about an axis 28 parallel to the longitudinal axis 29 through the switch device. The spacing of the rotational axis 28 from the longitudinal axis 29 is approximately .5.

The switch contacts are to remain open during revolving movement of the switch device about the axis 28 until the speed reaches 1800 rpm. and the contacts are to reopen .when the rotational speed falls about r.p.m. below this value. The switch is to be capable of repeating this Operation after being subjected to a mechanical shock of 13,000 Gs; also, the switch must be capable of withstanding storage up to ten years duration under all environments of temperatures from .80 F. to 170 F. and of humidity from .5% to 95 The stringent requirements of avoiding any switch misoperation under heavy conditions of shock and vibration, and of then operating dependably under the above-specified rotational conditions have been met reliably by securing the contact mass t0 the case through a helical spring wound tightly on itself so that it is pretensioned and serves as a rigid column until a specified centrifugal force is applied to the mass. For example, the pretensioning of the spring 23 enables it to supportthe mass 20 as a rigid column without any sidewise deflection from centrifugal force until the specified rotational speed is reached causing a sudden opening of the s spring convolutions. This is illustrated by the plot in FIG. 4 showing that the mass 20 is held stationary with respect to the case as the centrifugal force builds up to about 25 Gs, and that with 'increasing centrifugal force there is a rapid, sharp llexure of the spring indicated by the curved line 30. Without the pretensioning of the spring the mass would be moved gradually with increasing centrifugal force indicated by the straight line 31 with a resultant indefinite contact closure.

I claim:

1. A centrifugal switch comprising a metal case mounted: for revolving .movement Vabout Va givenV 'rota'-V tional axis, a mass in said case spaced from the walls thereof, a yieldable support in said case for said mass comprising a pretensioned helical spring secured at one end to said case and at the other end to said mass on a medial axis through said case parallel to said given rotational axis whereby said mass is deflected with side- Wise beinding of said helical spring when the centrifugal force of the mass reaches a critical value determined by the pretensioning of said spring, a first terminal pin insulatedly mounted in a wall of said case and having an end contact at said medial plane coacting wiith a contact area on said mass forming an electric switch operable by said deflection of the mass, and a second terminal pin on said case for said switch connected to said contact area via said case, helical spring and conductive surface of said mass.

2. The centrifugal switch set forth in claim 1 wherein said case comprises a cylindrical cup and a header fitted in the open end of said cup and welded thereto, and wherein said helical spring iis secured to said header.

3. The centrifugal switch set forth in claim 2 wherein said mass is a conductive body of cylindrical sha-pe supported with clearance on all sides from said case, said mass having a reduced diameter portion on one end wall extending toward said header and said header having an opening surrounded by a rim flange of te diameter of said reduced portion of said mass, and said helical spring being fitted onto and secured to said reduced diameter portion at one end of said rim flange at the other end.

4. The centrifugal switch set forth in claim 2 wherein said case is evacuated of air and filled with an inert gas, and wherein the surfaces in said case completing the circuit of said switch a-re plated with a noble metal.

5. A centrifugal switch having a metal cylindrical case mounted for revolving movement about a given rotational axis parallel to the longitudinal axis of the case, said case comprising a cylindrical cup provided with a rim flange and a metal header fitted into the open end of said cup against said rim flange and joined in sealed relation thereto, said header having a central opening, a cylindrical conductive mass in said case having an axial opening, a helical spring mounted at one end on an end wall of said case and secured at the other end to said mass for supporting said mass in a centered position in said case spaced from the walls thereof, said spring being pretensioned to constitute a rigid column for holding said mass fixed in said case until the centrifugal force on the mass reaches a critical value, a first terminal pin extending through said opening of said header and into said axial opening of said mass in spaced relation thereto, sai-d pin being hermetically sealed to said header and having an end portion forming a switch Contact coacting with the surrounding contact wall of said axial opening, and a second terminal electrically connected to said case.

6. The centrifugal switch set forth in claim 5 4wherein the opening in said header is surrounded by an inwardly extending rim flange, said axial opening in said mass is extended throughout the length thereof, said helical spring is fitted at one end onto said rim flange of said header, and said first terminal pin is extended substantially through the full length of the axial opening of said mass and is flanged at the end thereof forming a circular switch contact coacting with the sourrounding wall of said axial opening forming a set of normally open switch contacts closed by sidewise deflection of said mass when the centrifugal force on said mass reaches said critical value causing said helical spring to be bent sidewise.

References Cited UNITED STATES PATENTS 4/1935 Arden 200`80 5/ 1960 Patterson 200-80 U.S. Cl. XR. 102-70.2 

